Upgrade events

• Update to uWS v18.0.0; adding upgrade event:
  • Removes req from open event (breaking change)
  • Pass data from upgrade event to open event by calling res.upgrade with the user data object
• Adds Upgrade and UpgradeAsync examples showing these features.
• Updates old examples for compatibility.
• µWebSockets and µWebSockets.js now share the same major version number.